Voltage equalization method for use in radiofrequency switch having multiple transistors connected in series and radiofrequency switch

ABSTRACT

A voltage equalization method for use in a radiofrequency switch having multiple transistors connected in series and the radiofrequency switch. In the voltage equalization method, capacitors are additionally provided as parasitic capacitances between source electrodes and drain electrodes of transistors (M 1 -MN) connected in series to compose a radiofrequency switch, and voltage drop uniformity is implemented for the transistors (M 1 -MN) by adjusting the parasitic capacitances of the transistors (M 1 -MN). By means of different combinations of the positions, sizes, and spacing of metal bars on a first metal layer ( 1 ) and on a second metal layer ( 2 ), the parasitic capacitances between the source electrodes and the drain electrodes of the transistors (M 1 -MN) can be finely adjusted, thus increasing the voltage drop uniformity of the transistors (M 1 -MN). The method uses less transistors to accomplish the design of the radiofrequency switch.

BACKGROUND Technical Field

The present invention relates to a voltage equalization method, and inparticular to a voltage equalization method for use in a radiofrequencyswitch having multiple transistors connected in series as well as aradiofrequency switch adopting the voltage equalization method and acorresponding communication terminal, which belong to the technicalfield of radiofrequency integrated circuits.

Related Art

In a transmitting and receiving circuit of a communication system, aswitching technique is usually adopted to allow transmitting andreceiving channels to share the same antenna, so that the size andredundancy of the circuit are reduced. A radiofrequency switch is one ofcontrol devices for controlling radiofrequency signal transmission pathsand signal strength, and is applied widely in a lot of fields, such aswireless communication, electronic countermeasures, radar systems, etc.At present, in the field of high-power radiofrequency integratedcircuits, a radiofrequency switch composed of multiple transistorsconnected in series (multi-series transistor radiofrequency switch forshort) is often adopted.

As shown in FIG. 1, sources and drains of N transistors (M1-MN) of aradiofrequency switch composed of multiple transistors connected inseries are connected in sequence to form a series structure.Specifically, the source (or drain) of the first transistor is connectedto a radiofrequency signal input end RFin, and the source (or drain) ofthe last transistor is connected to a radiofrequency signal output endRFout. After the radiofrequency switch is opened, voltage between aradiofrequency signal input end and a radiofrequency signal output endwill drop onto a whole series transistor chain, and partial voltage(VI-VN) will be shared between the source and the drain of eachtransistor. The more the number of the transistors is, the lower thevoltage shared between the source and the drain of each transistor isand the less easily the transistors may be broken down. However, due tothe gradual drop of voltage from each transistor, the difference ofparasitic capacitors between the transistors and other reasons, thevoltage shared by each transistor is different. In order to prevent thebreakdown of the transistors, it is necessary to increase the number ofthe transistors, so that the transistors sharing the highest voltageenter a safe voltage range.

In Chinese Patent Application with the application No. 201410858446.8,Skyworks provides a radiofrequency switch module, which includes apackaging substrate configured to accommodate multiple components; and asemiconductor die mounted on the packaging substrate. The semiconductordie includes a switching device with multiple switching elements. Themultiple switching elements are connected in series to form a stack. Theswitching element has a nonuniform distribution of parameters, and thenonuniform distribution of the parameters enables the stack to have oneor more of first voltage processing capability higher than secondvoltage processing capability of a similar stack with the substantiallyuniform distribution of the parameters, a first ON resistance value lessthan a second ON resistance value of the similar stack and first linearperformance better than second linear performance of the similar stack.

SUMMARY

The primary technical problem which the present invention needs to solveis to provide a voltage equalization method for a multi-transistorseries radiofrequency switch.

Another technical problem which the present invention needs to solve isto provide a radiofrequency switch adopting the voltage equalizationmethod and a corresponding communication terminal.

In order to achieve the foregoing purpose, the present invention adoptsthe following technical solution:

According to a first aspect of the embodiments of the present invention,a voltage equalization method for a multi-transistor seriesradiofrequency switch is provided. In the method, a capacitor is addedas a parasitic capacitor between a source and a drain of each oftransistors connected in series to form the radiofrequency switch, andby adjusting the parasitic capacitor of each transistor, the voltagedrop uniformity of each transistor is achieved.

Preferably, the parasitic capacitor is implemented by a metal striparranged on each transistor and a respective metal layer of eachtransistor.

Preferably, sources and drains of N transistors of the radiofrequencyswitch are connected in sequence to form a series structure includingN+1 nodes.

Each node is connected to a first metal strip on a metal layer 1 througha metal and silicon contact hole, moreover, a metal layer 2 is providedwith one or more second metal strips, and the second metal strip isconnected to part of the first metal strip; and the first metal strips,the second metal strips and the N+1 nodes compose N parasiticcapacitors; and by adjusting the size and gap of the first metal strips,the size and gap of the second metal strips and a positional relationbetween the first metal strips and the second metal strips, the sizes ofthe N parasitic capacitors are adjusted respectively, where N is apositive integer.

Preferably, the size of the metal strips is increased/decreased in agrid width direction to enlarge/reduce the area of the parasiticcapacitor between the metal strips, so that the parasitic capacitor isenlarged/reduced.

Preferably, the gap between the metal strips is enlarged/reduced in agrid length direction to enlarge/reduce a gap between capacitor plates,so that the parasitic capacitor is reduced/enlarged.

Preferably, there are M second metal strips, which are respectively inperpendicular connection with previous M first metal strips on the metallayer 1, where M is a positive integer and not greater than N.

Preferably, there are M second metal strips, which are kept in asuspended state; and the second metal strips are distributed in the gapsbetween the first metal strips in a horizontal direction, and slightlyoverlap or do not overlap the first metal strips at edges of the metalstrips in a vertical direction.

Preferably, there are M second metal strips, which are connectedrespectively to M first metal strips in the metal layer 1, so that the Msecond metal strips and N+1-M metal strips in the metal layer 1 composeinterlayer parasitic capacitors, where M is a positive integer and notgreater than N.

According to a second aspect of the embodiments of the presentinvention, a radiofrequency switch is provided, which is composed bysequentially connecting sources and drains of multiple transistors, andthe radiofrequency switch adopts the above voltage equalization methodto achieve the voltage drop uniformity of each transistor.

According to a third aspect of the embodiments of the present invention,a communication terminal is provided, which includes the aboveradiofrequency switch.

Compared with the prior art, the voltage equalization method provided bythe present invention can finely adjust the parasitic capacitor betweenthe source and the drain of each transistor through differentcombinations of the positions, sizes and gaps of the metal strips on afirst metal layer and a second metal layer, thus increasing the voltagedrop uniformity of each transistor. By utilizing the present invention,fewer transistors can be used to carry out the design of theradiofrequency switch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a principle diagram of a radiofrequency switch composed ofmultiple transistors connected in series in the prior art;

FIG. 2 is a principle diagram of a radiofrequency switch added withparasitic capacitors in the present invention;

FIG. 3 is a working principle diagram of parasitic capacitorcompensation in an embodiment 1 of the present invention;

FIG. 4 is a working principle diagram of parasitic capacitorcompensation in an embodiment 2 of the present invention;

FIG. 5 is a working principle diagram of parasitic capacitorcompensation in an embodiment 3 of the present invention;

FIG. 6 is a working principle diagram of parasitic capacitorcompensation in an embodiment 4 of the present invention.

DETAILED DESCRIPTION

The technical content of the present invention will be described indetail below with reference to the drawings and the specificembodiments.

In the prior art, as a multi-transistor series radiofrequency switchcannot sufficiently utilize the voltage withstanding capability of eachtransistor and the area of the radiofrequency switch is large, theapplication range is greatly limited. Therefore, the present inventioncreatively adopts a variety of parasitic capacitor distribution methodsfor compensating voltage shared by each transistor in themulti-transistor series radiofrequency switch, so that the voltageshared by each transistor on a transistor chain is identical or similar,and thereby fewer transistors can be used to carry out the function ofthe radiofrequency switch.

As shown in FIG. 2, sources and drains (S/D) of N transistors (M1-MN) ofa radiofrequency switch composed of multiple transistors connected inseries are connected in sequence to form a series structure, where grids(G) are connected to the same control signal. The source (or drain) ofM1 is connected to a radiofrequency signal input end RFin, and the drain(or source) of MN is connected to a radiofrequency signal output endRFout. When the radiofrequency switch is off, voltage between theradiofrequency signal input end and the radiofrequency signal output endwill drop onto a whole series transistor chain, and partial voltage(VI-VN) will be shared between the source and the drain of eachtransistor. On the basis of utilizing an inherent capacitor between thesource and the drain of each transistor in the multi-transistor seriesradiofrequency switch, the voltage equalization method provided by thepresent invention further adds a capacitor CC1-CCN (N is a positiveinteger, similarly hereinafter) as a parasitic capacitor between thesource and the drain of each transistor. Through the flexible adjustmentand compensation of the parasitic capacitors, the voltage shared by eachtransistor on the transistor chain is identical or similar as much aspossible.

In one embodiment of the present invention, the parasitic capacitorsCC1-CCN are implemented by metal strips arranged on the transistors andrespective metal layers of the transistors. The detailed description isas follows: As the N transistors are connected in series, there are N+1source nodes and drain nodes in total, and each node is connected to theN+1 metal strips on a metal layer 1 (a first metal layer) through ametal and silicon contact hole. There are one or more metal strips on ametal layer 2 (a second metal layer). By adjusting the size and gap ofthe metal strips on the metal layer 1, the size and gap of the metalstrips on the metal layer 2 and a positional relation between the metalstrips on the metal layer 1 and the metal layer 2, the parasiticcapacitors CC1-CCN between the N+1 nodes can be adjusted, and therebythe voltage dropping onto the source and the drain of each transistor isequalized.

FIG. 3 to FIG. 6 respectively show a working principle diagram ofparasitic capacitor compensation in the different embodiments of thepresent invention. This will be described in detail below.

Embodiment 1

As shown in FIG. 3, the metal layer 1 is provided with N+1 metal stripswhich are respectively in perpendicular connection with the N+1 nodes ofthe transistor chain, and N+1 metal strips on the metal layer 2 arerespectively in perpendicular connection with the N+1 metal strips onthe metal layer 1. In this method, parasitic capacitors of the samelayer of metal are formed between the metal strips on the metal layer 1and the metal layer 2. By adjusting the sizes and gaps of the metalstrips on the metal layer 1 and the metal layer 2, the sizes of theparasitic capacitors between the nodes can be changed. Increasing thesize of the metal strips in a grid width direction can enlarge the areaof the parasitic capacitor between the metal strips, so that theparasitic capacitor is enlarged; otherwise, decreasing the size canreduce the parasitic capacitor. Increasing the gap between the metalstrips in a grid length direction is equivalent to increasing a gapbetween capacitor plates, so that the parasitic capacitor can bereduced; and otherwise, decreasing the gap can enlarge the parasiticcapacitor.

Embodiment 2

As shown in FIG. 4, the metal layer 1 is provided with N+1 metal stripswhich are respectively in perpendicular connection with N+1 nodes of atransistor chain, and M (M is a positive integer, similarly hereinafter)metal strips on the metal layer 2 are respectively in perpendicularconnection with the previous M metal strips on the metal layer 1. Inthis method, parasitic capacitors of the same layer of metal are onlyadded on the previous M nodes, and because voltage shared by theprevious transistors is usually low, more parasitic capacitors need tobe added to increase the shared voltage. The parasitic capacitors usedin this method are the same parasitic capacitors of the same layer ofmetal as that in embodiment 1, so the adjustment method is the same.

Embodiment 3

As shown in FIG. 5, the metal layer 1 is provided with N+1 metal stripswhich are respectively in perpendicular connection with N+1 nodes of atransistor chain, M metal strips on the metal layer 2 are kept in asuspended state, the metal strips on the metal layer 2 are distributedin the gaps between the metal strips on the metal layer 1 in ahorizontal direction, and in a vertical direction, the metal strips onthe metal layer 2 and the metal layer 1 can be overlapped at edges ofthe metal strips or are not overlapped. In this method, a main capacitorimplementation method is to introduce interlayer capacitors formedbetween the metal strips of the metal layer 1 and the metal layer 2between the nodes for compensation. In general, an interlayer parasiticcapacitor is smaller than an intra-layer inter-metal parasiticcapacitor, so this method mainly uses the parasitic capacitors on themetal layer 1 for major compensation and the parasitic capacitors on themetal layer 2 for minor adjustment. The adjustment of the size and gapof the metal strips in the metal layer 1 is the same as that in theembodiment 1 and the embodiment 2. By adjusting the size of the metalstrips in the metal layer 2 and a positional relation between the metalstrips in the metal layer 2 and the metal strips in the metal layer 1,if the metal strips in the metal layer 2 and the metal strips on themetal layer 1 more overlap or are closer to each other in the verticaldirection, the introduced parasitic capacitors will be bigger; andotherwise, the parasitic capacitors will be smaller.

Embodiment 4

As shown in FIG. 6, the metal layer 1 is provided with N+1 metal stripswhich are respectively in perpendicular connection with N+1 nodes of atransistor chain, the metal layer 2 is provided with M metal stripswhich are connected to M metal strips in the metal layer 1, and the Mmetal strips of the metal layer 2 and the N+1-M metal strips in themetal layer 1 compose interlayer parasitic capacitors. In this method,the distribution of the capacitors is more disperse, and only theinter-node capacitors distributed at different positions on the metallayer 2 undergo minor adjustment, while major compensation is mainlycarried out by the capacitors of the metal layer 1. The adjustmentmethod is the same as that in the embodiment 1, the embodiment 2 and theembodiment 3. For intra-layer parasitic capacitors, increasing the sizeof the metal strips in a grid width direction can enlarge the parasiticcapacitor; otherwise, decreasing the size can reduce the parasiticcapacitor. Increasing a gap between the metal strips in a grid lengthdirection is equivalent to increasing a gap between capacitor plates, sothat the parasitic capacitor can be reduced; otherwise, decreasing thegap can enlarge the parasitic capacitor. For the interlayer parasiticcapacitors, by adjusting the size of the metal strips in the metal layer2 and a positional relation between the metal strips in the metal layer2 and the metal strips in the metal layer 1, if the metal strips in themetal layer 2 and the metal strips on the metal layer 1 more overlap orare closer to each other in the vertical direction, the introducedparasitic capacitors will be bigger; and otherwise, the smaller theparasitic capacitors will be.

It should be noted that by the parasitic capacitor adjustment methodsprovided by the embodiment 1, the embodiment 2, the embodiment 3 and theembodiment 4 in combination with a device parasitic parameter simulationtool, each parasitic capacitor between the nodes can be adjusted finely,consequently, the equalization of the voltage of each transistor pointis realized, the voltage withstanding capability of each transistor isutilized sufficiently, the number of the transistors is decreased, andthe area of the radiofrequency switch is reduced. An experiment provesthat when fourteen series transistors are used to produce a transistorchain as the radiofrequency switch, the voltage equalization methodprovided by the present invention is adopted, parasitic parametersimulation software is used to simulate the parasitic parameter of eachnode, and node voltages are normalized, where a standard value is 100%.The comparison of experiment results is as follows: when the voltageequalization method provided by the present invention is not used foradjustment, voltage difference between the nodes is between 77% and185%; and after the voltage equalization method provided by the presentinvention is used for adjustment, the voltage difference between thenodes is between 97.2% and 103.7%. By comparison, the voltageequalization method provided by the present invention can effectivelyequalize internal voltages in the multi-transistor series radiofrequencyswitch.

Compared with the prior art, the voltage equalization method provided bythe present invention can finely adjust the parasitic capacitor betweenthe source and the drain of each transistor through the differentcombinations of the positions, sizes and gaps of the metal strips on themetal layer 1 and the metal layer 2, thus increasing the voltage dropuniformity of each transistor. By utilizing the present invention, fewertransistors can be used to carry out the design of the radiofrequencyswitch.

The voltage equalization method shown in the above embodiments can beused in a radiofrequency switch chip. Sources and drains of multipletransistors are connected in sequence to compose the radiofrequencyswitch chip. The specific structure of the radiofrequency switch chip isnot described in detail herein anymore.

In addition, the above radiofrequency switch chip can be used in acommunication terminal to serve as an important component of aradiofrequency integrated circuit. The communication terminal mentionedherein means a computer device supporting a variety of communicationsystems (such as GSM, EDGE, TD_SCDMA, TDD_LTE, FDD_LTE, etc.) which canbe used in mobile environment, including a mobile phone, a laptop, atablet personal computer, an on-board computer, etc. In addition, thetechnical solution provided by the present invention is also applicableto other places applying radiofrequency integrated circuits, such ascommunication base stations, etc.

The voltage equalization method for a multi-transistor seriesradiofrequency switch and the radiofrequency switch which are providedby the present invention have been described in detail above. For aperson of ordinary skill in the art, any apparent change made thereonwithout departing from the essence of the present invention shall beconsidered a violation of the patent right of the present invention, andshall bear a corresponding legal responsibility.

1. A voltage equalization method for a multi-transistor seriesradiofrequency switch, wherein a capacitor is added as a parasiticcapacitor between a source and a drain of each of transistors connectedin series to form the radiofrequency switch, and by adjusting theparasitic capacitor of each transistor, the voltage drop uniformity ofeach transistor is achieved.
 2. The voltage equalization methodaccording to claim 1, wherein the parasitic capacitor is implemented bya metal strip arranged on each transistor and a respective metal layerof each transistor.
 3. The voltage equalization method according toclaim 2, wherein sources and drains of N transistors of theradiofrequency switch are connected in sequence to form a seriesstructure comprising N+1 nodes; each node is connected to a first metalstrip on a first metal layer through a metal and silicon contact hole,moreover, a second metal layer is provided with one or more second metalstrips, and the second metal strip is connected to part of the firstmetal strip; the first metal strips, the second metal strips and the N+1nodes compose N parasitic capacitors; and by adjusting the size and gapof the first metal strips, the size and gap of the second metal stripsand a positional relation between the first metal strips and the secondmetal strips, the sizes of the N parasitic capacitors are adjustedrespectively, wherein N is a positive integer.
 4. The voltageequalization method according to claim 3, wherein the size of the metalstrips is increased/decreased in a grid width direction toenlarge/reduce the area of the parasitic capacitor between the metalstrips, so that the parasitic capacitor is enlarged/reduced.
 5. Thevoltage equalization method according to claim 3, wherein the gapbetween the metal strips is enlarged/reduced in a grid length directionto enlarge/reduce a gap between capacitor plates, so that the parasiticcapacitor is reduced/enlarged.
 6. The voltage equalization methodaccording to claim 4, wherein there are M second metal strips, which arerespectively in perpendicular connection with previous M first metalstrips on the first metal layer, wherein M is a positive integer and notgreater than N.
 7. The voltage equalization method according to claim 4,wherein there are M second metal strips, which are kept in a suspendedstate; and the second metal strips are distributed in the gaps betweenthe first metal strips in a horizontal direction, and slightly overlapor do not overlap the first metal strips at edges of the metal strips ina vertical direction.
 8. The voltage equalization method according toclaim 4, wherein there are M second metal strips, which are connectedrespectively to M first metal strips in the first metal layer, so thatthe M second metal strips and N+1-M metal strips in the first metallayer compose interlayer parasitic capacitors, wherein M is a positiveinteger and not greater than N.
 9. A radiofrequency switch, composed bysequentially connecting sources and drains of a plurality oftransistors, wherein the voltage equalization method according to claim1 is adopted to achieve the voltage drop uniformity of each transistor.10. A communication terminal, wherein the communication terminalcomprises the radiofrequency switch according to claim
 9. 11. Thevoltage equalization method according to claim 5, wherein there are Msecond metal strips, which are respectively in perpendicular connectionwith previous M first metal strips on the first metal layer, wherein Mis a positive integer and not greater than N.
 12. The voltageequalization method according to claim 5, wherein there are M secondmetal strips, which are kept in a suspended state; and the second metalstrips are distributed in the gaps between the first metal strips in ahorizontal direction, and slightly overlap or do not overlap the firstmetal strips at edges of the metal strips in a vertical direction. 13.The voltage equalization method according to claim 5, wherein there areM second metal strips, which are connected respectively to M first metalstrips in the first metal layer, so that the M second metal strips andN+1-M metal strips in the first metal layer compose interlayer parasiticcapacitors, wherein M is a positive integer and not greater than N.